Telecommunications terminal block

ABSTRACT

Insulation displacing connectors of an &#34;inverted&#34; type extend upwardly from a base of the terminal block into connector chambers of driver modules movable relative to the base between upper and lower positions. Passageways within the modules direct service wires moved through the passageways into the connector chambers and into entrance openings underlying upper edge portions of the insulation displacing connectors within the chambers. Movement of the module from its upper position to its lower position drives the service wires downwardly from the entrance openings of the connectors into and through slots underlying the entrance openings, to establish electrical contact with the service.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/046,059, filed12 Apr. 1993, U.S. Pat. No. 5,557,250, which is a continuation-in-partof application Ser. No. 07/906,803, filed 30 Jun. 1992 abandoned; and ofapplication Ser. No. 07/906,952, filed 30 Jun. 1992 abandoned; and ofapplication Ser. No. 07/954,612, filed 30 Sep. 1992, abandoned, which isa continuation of application Ser. No. 07/776,501, filed 11 Oct. 1991,abandoned.

FIELD OF THE INVENTION

This invention relates to terminal blocks used by telecommunicationcompanies to connect conductor wires of a multicore cable to servicewires that extend to customer residences or places of business. Theinvention more specifically relates to an improved terminal block of thetype that contains viscous sealant material.

BACKGROUND OF THE INVENTION

A terminal block of the aforesaid type is usually mounted outdoors. Evenwhen surrounded by a protective housing, it is exposed to rain, snow,sleet, ice, temperature fluctuations, dirt, insect infestation andsimilar conditions that may adversely affect the electrical connectionsbetween the service wires and electrical connectors, which may be andusually are of the insulation displacing type, within the blocks. Tominimize incursion of foreign matter, viscous sealing material hasheretofore been provided within interior areas of prior art terminalblocks. The protection afforded by the sealant material usually isadequate for as long as the original connections between the servicewires and the associated insulation displacing connectors remainundisturbed, but has heretofore rapidly decreased in proportion to thenumber of times that the connections are re-entered (i.e, broken andreestablished) by a telecommunications craftsperson. The decreasingprotection is due to the fact that each re-entry displaces some of thesealant and causes the formation therein of voids that permit ingress ofair, dirt, moisture, insects and the like. The use of sealant of the geltype minimizes the size of such voids but does not entirely eliminatetheir formation. Reliable protection of the terminal block against surge(i.e., overvoltage and/or overcurrent) conditions is also highlydesirable since in the absence of such protection lightning strikes,engagement of the telephone wires by power lines, or similar conditionscan severely damage the terminal block and components or structuresadjacent thereto and/or connected therewith.

SUMMARY OF THE INVENTION

The present invention provides an improved telecommunications terminalblock, of the type containing protective viscous sealant material, thatis of compact, durable and economical construction; can be re-entered anumber of times without significant decrease in the efficacy of theprotection afforded by the sealant material; provides surge protectionwhen that is desired; and that can be readily installed and used by acraftsperson upon a telephone pole or in other exposed locations toconnect service wires having a wide range of gauges.

In its preferred embodiment the terminal block includes an elongate basethat is adapted to be secured to a telephone pole or other supportivestructure, and further includes at least one and usually a plurality ofdriver modules that are cantilever mounted upon the base in laterallyadjacent relationship to each other for individual movement relative tothe base between first (illustratively upper) and second (illustrativelylower) positions respectively distal from and adjacent to the base.Movement of each module between its first and second positionspreferably is effected by a threaded fastener that extends through anopening in a mounting chamber of the module and into a base within anunderlying mounting post of the base. A plurality of pairs of insulationdisplacing connectors, which may be and preferably are of an "inverted"type, project upwardly from the base at spaced intervals along itslength. Lower portions of the connectors are pre-joined to appropriateones of the wires of a multi-core cable that extends into an interiorpart of the base filled with conventional potting material. The sectionsof the paired first and second connectors projecting from the baseextend into respective first and second connector chambers of anoverlying one of the driver modules upon the base. First and second pumpchambers within the driver module communicate with respective ones ofthe connector chambers. First and second passageways extending from anouter surface of the module into the connector chambers direct the endsof first and second insulated service wires, that are inserted into andadvanced longitudinally of such passageways by a craftsperson while themodule occupies its upper position, into respective first and secondones of the chambers and into entrance openings of respective first andsecond ones of the insulating displacing connectors within the chambers.Movement of the driver module from its upper position to its lowerposition displaces the two insulated service wires downwardly into slotsof the connectors and establishes electrical contact with respectiveones of the connectors. In the case of heavily insulated service wires,the downward module movement also impales the insulation of the servicewires upon retainer elements that underlie the slots and resist axialpull-out of the wires. The connector chambers, pump chambers and servicewire passageways of each module contain protective sealant material,which preferably is of the gel type. Each module may include anelectrical surge protector device which is both fail safe and vent safe,and which preferably is located in a space that also contains protectivesealant material.

Each entry of the module disturbs the sealant to some extent, and maycreate undesirable voids therein. Sealant pump means are provided tocompensate for the sealant disturbance, and to eliminate or at leastreduce the size of voids created thereby in the sealant. In oneembodiment the pump means includes first and second sealant pumpchambers that are located in each driver module, communicate withrespective first and second ones of the connector chambers and theservice wire passageways of the module, and that contain reservesealant.

The sealant pump means further includes pump piston elements that extendupwardly from the base of the terminal block into aligned ones of thepump chambers of an overlying driver module upon movement of the modulefrom its upper position to its lower position. The aforesaid pump meansdrives enough reserve sealant material from the pump chambers into theconnector chambers and service wire passageways as to eliminate or atleast reduce the size of any voids present therein by reason of priorre-entries. The downward module movement also causes tip and ringcontacts upon the surge protector device to engage contacts upon theinsulation displacing connectors, and also grounds a third contact ofthe surge protector. In another embodiment tip and ring contacts uponthe surge protector continuously engage respective ones of theinsulation displacing connectors, and a third contact of the surgeprotector continuously engages ground, except when grounding of theprotector is not desired, irrespective of the vertical position of themodule. When surge protection is not included, a non conductive studextends downwardly from the member that normally carries the surgeprotector and is received within an underlying slot in the basecomponent of the terminal block, which usually houses the grounding bus.Interference between the grounding bus and the stud preventsmisapplication. An upstanding flexible collarlike member upon the postcontaining the bore that receives the threaded fastener that impartsvertical movement to the driver module engages the undersurface of suchscrew and resiliently supports the same such as to permit the initialthreads to be formed in the bore with only minimal downward forceapplied to the screw. This reduces the possibility of undesirable"stripping" of the internal screw threads of the bore.

At least part of each driver module preferably is formed of transparentmaterial permitting exterior viewing of interior components, such as theaforesaid overvoltage limiting device, and monitoring of the correctinsertion of the insulated service wires within the connector chambersand connector members of such driver module.

In one embodiment engageable and disengageable latch means, whichincludes cooperating latch elements upon each module and upon the baseof the terminal block, prevent inadvertent complete removal of a modulefrom the base and provide tactile feedback of the module's arrival atits upper position. In a second embodiment a detent element providestactile and/or audible indication of the position of the module, andprevent inadvertent removal.

The fastener that drives each module is sequestered from the sealantmaterial within the module so as to not shear or otherwise disturb thesealant.

Each of the insulation displacing connectors preferably is of an"inverted" type having an upper edge portion that extends between andinterconnects upper ends of opposite side edge portions of theconnector. A service wire entrance opening in adjacent underlyingrelationship to the aforesaid upper edge portion of the connector isadapted to initially receive, preferably at an angle of about 60°, theinsulated service wire associated with the connector. Each service wireis displaced downwardly from the aforesaid entrance opening into andthrough a slot extending downwardly from the opening and havinglongitudinal sections of successively narrower width. A tooth-shapedretainer element underlying the slot impales the insulation upon, andthus resists axial pull-out of, a heavily insulated service wire. Eachconnector may also have a contact that is engaged by a contact of thesurge protector device when the module occupies its lower position.Alternatively each connector may be engaged continuously by contacts ofa surge protector.

In one embodiment an upper edge portion of at least one of the twoconnector chambers of each driver module preferably has a section thatslopes so as to cause a thereto connected test clip to extend angularlyaway from the chamber and from a test clip upon the adjacent chamber.This prevents shorting of the clips against each other. In anotherembodiment the upper test port portion of one of the chambers containingthe insulation displacing connectors is bordered by a wall that slopesor is otherwise so shaped as to prevent attachment of a test clip to it.This decreases the possibility of inadvertent placement of test clips soas to make electrical contact with the conductive blade. A similarresult is achieved in still another embodiment by providing a shoulderintermediate the length of a test clip receiving wall bordering adjacenttest ports.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a terminal block in accordancewith the invention and of service wires extending into driver modulesthereof, the rightmost driver module being shown in its upper positionand the remaining driver modules being shown in their lower positions;

FIG. 2 is a rear elevational view of the terminal block;

FIG. 3 is an enlarged vertical section taken substantially along theline and in the direction of the arrows 3--3 through the rightmostdriver module of FIG. 1, which is shown in its upper position, theassociated service wires being shown at a location preliminary to theirinsertion into the module;

FIG. 4 is a view similar to FIG. 3, but taken in the direction of thearrows 4--4 of FIG. 1 and showing the driver module and service wires intheir lower positions;

FIG. 5 is a front, right, top perspective view of the terminal blockwherein the right-most driver module and components thereof are shown inexploded relationship;

FIG. 6 is a bottom plan view of a driver module;

FIG. 7 is a view showing at its left side a top plan view of a drivermodule, at its right side a top plan view of the part of the baseunderlying a driver module, and showing in its central portion andprimarily in horizontal section components of the driver module and someassociated components carried by the base of the terminal block;

FIG. 8 is a front elevational view of one of the insulation displacingconnectors of the terminal block;

FIG. 9 is a laterally foreshortened view partially in elevation andpartially in vertical section of test clips secured to upper end testport sections of driver module connector chambers and therein disposedinsulation displacing connectors;

FIGS. 10a, b, and c are fragmentary front elevational views of theinsulation displacing connector of FIG. 8 showing sequential positionsoccupied by a heavily insulated service wire during movement thereoffrom an upper part to a lower part of the connector;

FIGS. 11a, b, and c are front elevational views of the connector of FIG.8, showing sequential positions occupied by a lightly insulated servicewire during movement thereof from an upper part to a lower part of theconnector, and also showing a conductor of the multi-wire bundle withinthe base of the terminal block;

FIG. 12 is a schematic illustration of a circuit having typicalthree-element gas discharge tube and a one-pair telecommunications line;

FIG. 13 is a sectional view of the gas tube of FIG. 12;

FIG. 14 is a sectional view of a known type of gas tube equipped with anair-gap type of vent safe device;

FIG. 15 is a diagram of the effect of oil and water upon the breakdownvoltage of the air-gap vent safe device shown in FIG. 14;

FIG. 16 is an exploded, somewhat schematic perspective view of a ventsafe device of the present invention in association with a gas tubeprotector;

FIG. 17 is a partially exploded elevational view of components of thevent safe assembly of FIG. 16; FIG. 18 is an enlarged fragmentary topperspective of the gas tube and ground electrode/retainer shown in FIGS.16 and 17;

FIG. 19 is a sectional view similar to FIG. 13 showing the vent safedevice of FIGS. 16-18 upon the gas tube;

FIG. 20 is a partially schematic sectional view of an embodiment inwhich the vent-safe device is spaced from but electrically connected tothe gas tube;

FIG. 21 is a sectional view of the gas tube and vent safe device of FIG.19 encapsulated in a gel;

FIGS. 22-24 are IV-curves for different thicknesses of nonlinearresistive films usable in the vent safe device;

FIG. 25 is the IV curve for a gas tube vent safe device of theconstruction shown in FIGS. 15-18 and used as a replacement for theair-gap of a commercially available three element gas tube vent safedevice;

FIG. 26 is the IV curve for a more conductive film;

FIG. 27 is an IV curve for a commercially available film;

FIGS. 28-30 depict the electrical impulse breakdown behavior of the FIG.27 film as a function of current loading;

FIG. 31 is a vertically exploded perspective view of a surge arrestorhaving a fail-safe thermal overload mechanism in accordance with theinvention;

FIG. 32 is an end view of the arrestor and components of the overloadmechanism in an assembled condition;

FIG. 33 is a side elevational view of the surge arrestor;

FIG. 34 is a top plan view of the assembly of FIG. 31, showing inphantom lines a solder billet whose opposite ends are spaced from lineelectrodes at opposite ends of the arrestor housing;

FIG. 35 is a view similar to FIG. 31 showing in phantom lines a solderbillet whose ends extend to electrodes at opposite ends of the body ofthe arrestor;

FIG. 36 is a fragmentary end view of the arrestor housing and of asolder billet and overlying channel member of the fail-safe mechanism;

FIG. 37 is a view similar to FIG. 36, but showing the components inpositions assumed during a thermal overload;

FIG. 38 is a view similar to FIG. 36 showing gel or other protectivesealant material encapsulating the arrestor and components of thefail-safe mechanism; FIG. 39 is a perspective view of another embodimentof a fail-safe mechanism for a surge protector;

FIG. 40 is a partially exploded front top perspective view of anotherembodiment of a terminal block, and of a support member underlying theterminal block;

FIG. 41 is a view primarily in front elevation, but partially invertical section, showing the terminal block of FIG. 40 in an assembledcondition;

FIG. 42 is a rear elevational view of the FIG. 41 terminal block;

FIG. 43 is an enlarged sectional view taken approximately along the line43 of FIG. 41 through one of the driver modules and the base of theterminal block of FIG. 41;

FIG. 44 is a view similar to FIG. 43 but taken along the line 44 of FIG.41 through a driver module in a lower position;

FIG. 45 is a view primarily in top plan, but with some components shownin section, of the terminal block of FIGS. 40-42;

FIG. 46 is an enlarged sectional view of the main body of one of thedriver modules of the terminal block of FIGS. 40-42;

FIG. 47 is a sectional view taken approximately along the line 47through the driver module body of FIG. 46;

FIG. 48 is an end elevational view of another embodiment of a fail-safedevice associated with a surge protector and an insulation displacingconnector;

FIG. 49 is a top plan view of the components of FIG. 48;

FIG. 50 is an exploded view, partially in vertical section and partiallyin side elevation, of an ungrounded embodiment of the terminal block;and

FIG. 51 is a view primarily in vertical section showing the componentsof FIG. 50 in assembled condition and with the driver module in a lowerposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terminal block identified in its entirety in FIGS. 1 and 2 by thenumeral 12 includes an elongate base 14 that may be of any desiredlength. Base 14 illustratively extends horizontally and is of generallyrectangular shape. A multi-core cable 16 extends into a rearward sectionof base 14 from one end of the base. A plurality of bosses 18 projectupwardly from base 14 at laterally spaced locations along its length.Each boss 18 has a low barrier wall 20 that extends transversely acrossa central part of the boss and rearwarcey from it. First and secondslots 22 upon opposite sides of the wall 20 of each boss 18 extendvertically through such boss and the upper wall of base 14. The firstand second slots 22 within each boss 18 respectively lie in generallyvertical first and second planes that extend in substantially paralleltransversely spaced relationship to each other, and in nonparallelrelationship to a vertical plane containing the longitudinal axis ofbase 14.

First and second insulation displacing connectors 24 extend verticallythrough respective ones of the first and second slots 22 in each boss18. Each connector 24 preferably is formed of beryllium copper alloy No.C17200 that has an extra hard temper and a minimum yield of 165 Ksi. Thelower section of each connector 24 within base 14 is connected to anappropriate one of the wires 17 of cable 16, after which the interior ofthe base is filled with a suitable potting material. This preferably isdone at the location where bases 14 are fabricated.

As is best shown in FIGS. 8, 10 and 11, the part of each connector 24above base 14 has longitudinally extending opposite side edge portions26 that constitute primary spring elements of the connector. (Connector24 further has an upper edge portion 28 that interconnects the upperends of side edge portions 26 and stiffens them to such an extent as toeliminate the need for "stop" members that limit outward movement ofedge portions 26. A service wire entry opening 30 in adjacent underlyingrelationship to upper edge portion 28 extends transversely through eachconnector 24. Lower edge portions 31 of opening 30 have upwardly facingsharp cutting surfaces. A vertical slot 32 within the central part ofconnector 24 communicates at its upper end with opening 30 and extendsdownwardly from it. Slot 30 decreases in width from its upper to itslower end, and terminates above an upwardly extending pointed impalingelement 34 of the connector. The opposite sides of slot 32 are borderedby confronting edges of elongate secondary spring elements 38 thatextend downwardly in cantilever fashion from the upper part of connector24, have free rounded lower ends, and are bordered along most of theirlength by a generally kidney-shaped opening 42 of connector 24. Duringuse of connector 24, spring elements 26, 38 undergo resilient lateralbending movement. The secondary spring elements 38 also undergotorsional flexure about their longitudinal axes. A contact element 44having a downwardly sloping upper surface projects outwardly from eachconnector 24 below impaling element 34.

The illustrated connector 24 is particularly suited for use withinsulated service wires ranging from eighteen and one-half gauge coppercoated steel conductors through twenty-four gauge solid copper, and hasa thickness of about twenty-thousandths of an inch.

The entry opening 30 of each connector 24 is adapted to receive servicewires 46 as heavily insulated as that shown in FIGS. 1, 3, 4, and 10, oras lightly insulated as that of the service wire shown in FIG. 11.Whether heavily or lightly insulated, the service wires 46 introducedinto entry opening 30 of a connector 24 preferably define an entry anglewith the connector that is substantially less than 90° and preferably isabout 30°.

Referring now particularly to FIGS. 10a, 10b and 10c, the relativelyheavy insulation of the illustrated service wire 46 introduced intoopening 30 and then moved downwardly therefrom is initially cut by thesharp edges 31 adjacent the bottom of opening 30. As service wire 46 isdisplaced downwardly into and through slot 32, the thereto adjacentconfronting edges of secondary spring elements 38 engage, as shown inFIG. 10b, the central metal conductor of service wire 46. Final downwardmovement of the service wire impales its insulation upon the pointedimpaling element 34 underlying slot 32, as shown in FIG. 10c. Movementof the heavily insulated service wire 46 into and through slot 32deflects spring elements 26, 38 outwardly, and also causes torsionaldeflection of secondary spring elements 38. The torsional deflections ofspring elements 38 contribute significantly to the fact that suchelements are not strained beyond their elastic limits by passage ofheavily insulated service wires 46 through slot 32. Upon return movementof service wire 46 upwardly to opening 30 the spring elements thereforeresiliently return to their undeflected positions shown in FIGS. 8 and10a.

When the service wire 46 is relatively lightly insulated, such as shownin FIGS. 11a, 11b and 11c, downward movement thereof from entry opening30 into slot 32 occurs with little if any engagement between wire 46 andsharp edges 31 of opening 30. Substantially all of the cutting of theinsulation of the lightly insulated service wire is done by theconfronting edges of secondary spring elements 38. The primary springelements 26 undergo little if any deflection, and the lowermost positionof the lightly insulated service wire 46 is considerably above impalingelement 34, as shown in FIG. 11c. Service wires having insulation of asize intermediate that of the illustrated heavily and lightly insulatedwires 46 will produce spring element deflections intermediate thoseproduced by the wires shown in FIGS. 10 and 11.

Wires 17 of cable 16 are illustratively received within and connected tothe lower end section of respective ones of connectors 24,illustratively by generally T-shaped insulation displacing slots 19provided in connectors 24. The aforesaid connection preferably is madein the facility where the base 14 is manufactured, and is preferablythere surrounded by protective potting material shown in the lower partof FIGS. 3 and 4.

A plurality of driver modules 50 is mounted in laterally adjacentrelationship to each other along the length of base 14 for verticalmovement relative to the illustratively horizontally extending base andto each other between a first, illustratively upper position and asecond, illustratively lower position. The modules preferably are formedof transparent durable dielectric plastic such as LEXANR. Each module 50is cantilever mounted upon a rearward part of base 14 by mounting meansthat includes a mounting chamber 54 that is of U-shaped configuration asviewed in top plan and that is located within the rear part of themodule. The mounting means further includes an underlying mounting post56 that is of complementary U-shaped configuration and that extendsupwardly from base 14 into the therewith vertically aligned chamber 54.The mounting means further includes a rotatable fastener 58, whichillustratively and preferably is a threadformaing screw having a driverhead that overlies the upper surface of chamber 54. A threaded shank offastener 58 extends through a bore 60 in the chamber's top wall, acaptive washer 61 and into an initially unthreaded axially aligned borewithin the post 56 underlying chamber 54. Rotation of fastener 58 in theappropriate "tightening" direction forms screw threads in the bore ofpost 56 and drives module 50 downwardly from its upper position shown inFIG. 3 to its lower position, shown in FIG. 4, wherein the upper wall ofchamber 54 abuts the upper surface of mounting post 56. Return upwardmovement of module 50 is effected, when desired, by reverse rotation offastener 58. Canting or tilting of module 50 during and followingvertical movement thereof is prevented by, among other things, slidingengagement between the exterior surfaces of mounting post 56 and thecomplementarily shaped confronting inner surfaces of mounting chamber54.

Engageable and disengageable latch means prevent inadvertent removal ofeach driver module 50 from base 14, while permitting movement of themodule relative to the base from the module's upper position shown inFIG. 3 to its lower position shown in FIG. 4. The latch means includesresilient latch elements 62 that extend vertically in laterally spacedand generally parallel relationship to the front and rear surfaces ofeach module 50 and that are permanently connected intermediate theirlength to the module. The latch means further includes cooperating latchelements 64 that are connected to and extend forwardly and rearwardlyfrom base 14. During initial installation of a module 50 upon base 14,downward movement of the module causes the lower end of each latchelement 62 to engage a sloping cam surface upon an underlying latchelement 64. The elements 62 are cammed outwardly by such engagement, andthen resiliently return to a position beneath latch element 64. Thelatch elements 62, 64 then permit movement of the module 50 between itsupper position of FIG. 3 and its lower position of FIG. 4, but preventinadvertent complete withdrawal of the module from base 14. The latchesalso provide tactile feedback, in the form of increased resistance toreverse rotation of screw 58, that lets a telecommunicationscraftsperson know when a module reaches its upper position. Tactilefeedback indicating arrival of the module at its lower position isprovided by then increased resistance to tightening rotation of fastener58.

The first and second insulation displacing connectors 24 extendingthrough and upwardly from each boss 18 upon base 14 are received withinrespective first and second laterally adjacent connector chambers 66that extend vertically through each module 50. The two chambers 66 arelaterally separated from each other along part of their height by avertical barrier wall 90 best shown in FIG. 6. Wall 90 is formed ofdielectric plastic material and overlies the wall 20 of the adjacentboss 18 upon base 14. Chambers 66 are forwardly of and innon-communicating relationship with the module chamber 54 through whichfastener 58 extends. As is best shown in FIGS. 3 and 4, the width ofeach chamber 66 decreases with increasing distance from the lower end tothe upper end of the connector 24 within the chamber. Adjacent its upperend each chamber 66 has a test port area 66a into which a connector 24extends. The two connectors 24 within each module 50 lie in parallellaterally spaced vertical planes that extend in angular obliquerelationship to a vertical plane containing the longitudinal axis ofterminal block 12. When viewed perpendicularly to their major surfaces,i.e., in the direction of the arrow 68 of FIG. 7, the two connectors 24of each pair have overlapping side edge portions. The aforesaidorientations of the connectors relative to each other and to base 14contribute signficantly to the compact construction of terminal block12.

First and second laterally adjacent passageways 70 extend through thefront wall of each driver module 50 and into respective first and secondones of the chambers 66 containing insulation displacing connectors 24.When a telecommunication craftsperson inserts first and second servicewires 46 as far as they will go into respective first and second ones ofthe passageways 70 of a module 50 occupying its upper position, theleading ends of the customarily black service wires extend intorespective first and second ones of the module's chambers 66 and alsointo and through the entry openings 30 of respective first and secondones of the insulation displacing connectors 24 within chambers 66. Thetransparent construction of the module permits visual verification ofthe position of the wires, particularly when the module is eithercolorless or of a color other than black. When a module 50 is moveddownwardly from its upper position to its lower position, illustrativelyand preferably by rotation in the appropriate direction ofthread-forming fastener 58, each service wire 46 is moved downwardlyinto and through the slot 32 of the associated connector 24 to its finalposition adjacent the lower end of the slot and wherein its innermetallic conductor is in engagement with connector 24. The finalposition of a heavily insulated service wire 46 is below that of alightly insulated wire. This is due to the fact that a lightly insulatedwire is not engaged and moved downwardly by the upper surface of thesurrounding passageway 70 until after module 50 has moved downwardly asignificant extent. As previously noted, each heavily insulated servicewire 46 is also impaled in its lowermost position by the connector'simpaling element 34 which resists axial pull-out of the service wire.

Movement of module 50 to its lower position effects engagement of thelower end of each barrier wall 90 of the module with the upper end ofthe barrier wall 20 of the underlying boss 18 of base 14. Such movementof module 50 also downwardly displaces a component 72 thereof, bestshown in FIG. 5, from its upper position shown in FIG. 3 to its lowerposition shown in FIG. 4. When surge protection is desired, thecomponent 72 of each module contains a cylindrical fail-safe andvent-safe surge protector device 74. Device 74 has first and second tipand ring contacts 76 extending radially therefrom to locationsrespectively adjacent first and second ones of the insulation displacingconnectors 24. Device 74 also has an arcuate ground contact 78 upon itscylindrical outer surface. As shown in FIG. 4, downward movement ofcomponent 72 and device 74 brings tip and ring contacts 76 intoengagement with respective ones of the projecting contacts 44 upon firstand second ones of the connectors 24, and also brings the contact band78 of device 74 into engagement with an upwardly extending arm 80 of aground bus 81 that is mounted upon and extends longitudinally of base14. If for any reason surge protection is not desired, a device 74 nothaving a ground contact may be substituted for the illustrated device74. The ungrounded device (not shown) preferably is of a color clearlydifferent from that of the protector device 74. As is also shown in FIG.5, the service wire passageways 70 of each driver module 50 are definedin part by first and second channels 82 that extend through and openfrom the upper portion of module component 72 upon opposite sides of avertically extending partition 83 that laterally separates the servicewires within respective ones of the channels.

As is best shown in FIGS. 3 and 4, viscous protective sealant material84, which preferably is a gel of the type disclosed in U.S. Pat. Nos.4,634,207 and 4,864,725, is provided within and substantially fills thechambers 66, passageways 70 and the space about component 72 of eachdriver module 50. In conjunction with barrier walls 20, 907 sealant 84isolates the adjacent connectors 24 of a module 50 from each other andfrom the ambient environment, particularly when the module 50 occupiesits lower position. Since the sealant 84 within the front lower part ofmodule 50 then is closely adjacent base 14, such sealant and theunderlying part of the base similarly isolate surge protector device 74and the electrical contacts associated therewith from the ambientenvironment.

Movement of service wires 46 into and from a module may disturb thesealant material 84, particularly when the sealant is not a gel, andcause the formation of voids in it. Voids substantially reduce theprotection afforded by the sealant. The protection decreases inproportion to the number of re-entries, and in prior terminal blocksusing non-gel sealant may become deficient after a relatively smallnumber of reentries.

In order to eliminate or at least substantially reduce the size of voidsin the sealant material 84 within chambers 66, passageways 70 and othercritical areas of driver module 50, the block is provided with sealantpump means. The pump means includes first and second sealant pumpchambers 88 that extend upwardly through the bottom of each module 50 toan elevation at or (as shown) above that of service wire passageways 70,and that communicate with such passageways and through them withrespective first and second ones of the module's connector chambers 66.Chambers 88 contain reserve sealant material. Each chamber 88 has anarcuate rear wall that slidably engages and conforms to the curvature ofthe arcuate front wall of the thereto adjacent post 56 upon base 14. Thesealant pump means further includes first and second pump pistonelements 92 that extend upwardly from base 14 and, when the overlyingmodule 50 occupies its lower position shown in FIG. 4, into the openlower end portions of respective first and second ones of the module'spump chambers 88. Pump piston elements 92 each have peripheral front,rear and side surfaces that slidably and closely engage, and arecomplementary in shape to, the thereto confronting surfaces of theassociated pump chamber 88.

After service wires 46 are inserted into an upwardly positioned module50, downward movement of the module to its lower position of FIG. 4causes pump piston elements 92 to enter the lower end portions ofrespective overlying ones of the module's pump chambers 88. Thisdisplaces reserve sealant 84 from pump chambers 88 into connectorchambers 66, passageways 70 and other module areas (including thatcontaining surge protector device 74) communicating therewith. Suchdisplacement compresses the sealant material within the aforesaid areasand thereby eliminates or at least reduces the size of any voidstherein. This highly desirable result occurs automatically, whenever amodule 50 is re-entered, for as long as its pump chambers 88 containsufficient reserve sealant.

When a driver module 50 occupies its lower position as shown in FIG. 4,the upper ends of connectors 24 are located below the upper surface ofuppermost test port sections 66a of chambers 66, and below the uppersurface of the sealant material 84 therein. A telecommunicationscraftsperson attaching a test clip to the upper part of connector 24therefore must insert an end of the test clip into the sealant materialand, upon completion of the circuit testing, withdraw the test clip fromsuch material. Withdrawal of the test clip from association with aconventional insulation displacing connector, of the type having an openupper end, may cause withdrawal of some of the sealant material. Removalof sealant material 84 by a test clip applied to the upper end of one ofthe present insulation displacement connectors 24 is less likely tooccur since the upper edge portion 28 of the connector resists movementof the sealant with the test clip as the clip is withdrawn.

FIG. 9 shows test clips 94 that engage the upper edge portion 28 ofconnectors 24 and that each have a pin or tooth element 96 that extendsinto the opening 30 of the associated connector. This minimizes thepossibility of inadvertent slippage of test clips 94 from connectors 24.

As is also shown in FIG. 9, the upper edge portion of at least one(illustratively the leftmost one) of the two connector chambers 66 ofeach module 50 preferably is provided with a sloping portion 98 whichcauses the test clip 94 secured thereto to extend angularly outwardlyaway from the central axis of such chamber and away from a test clipsecured to the other chamber of the module. This minimizes thepossibility of contact between and shorting of the test clips.

In addition to its previously discussed functions, the sealant material84 surrounding and encapsulating surge protector device 74 protects thedevice's previously sealed air gap (not shown), or itself acts as adielectric when present in the gap.

FIGS. 12-30 of the drawings relate to a ventsafe apparatus for gas tubessuch as are used to protect telecommunications equipment from electricalinterference or damage resulting from high voltage lightning pulses. Agas contained in the tubes ionizes at high voltages to divert suchpulses to ground. The tubes also maintain a limited sustained ionizationin the presence of a continuing high current overload, such as from anaccidental power line crossover. To assure the performance of such tubesin the rare event that the ionizable gas vents from the tube, and to addprotection in the case of overheat failure during sustained over-currentconditions, prevailing industry practice is to require so-called"ventsafe" and "fail-safe" mechanisms along with the basic gas tubeprotector itself. (The term "vent-safe" now commonly refers to backupovervoltage protection if the gas "vents" or is lost to the atmosphere.The terra "failsafe" now commonly refers to thermal overload protection,although the term taken literally cloaks this connotation.)

Fail-safe protection is now commonly afforded by a fusible metallic orplastic material that, when heated due to the energy from the currentoverload, yields to a biased shorting member to provide a permanentcurrent shunt around the gas tube. Vent-safe protection is usuallyprovided by an air gap in the external structure of the device. The airgap is carefully dimensioned to require a firing potential considerablyabove the normal firing potential of the gas tube itself, so that aproperly functioning gas tube will prevent the air gap from firing. Thisis important since an overvoltage pulse usually fires harmlessly througha properly functioning gas tube, but may damage the air gap (which isintended only as a safety backup). Such air gaps are typically designedto fire at about twice the design firing voltage of the gas gap. Anexample of such a device may be found, for example, in U.S. Pat. No.4,212,047 (Napiorkowski, issued Jul. 8, 1980).

Unfortunately, it has been found that air gap vent-safe protectionschemes can become unreliable. Telecommunications installations areintended to remain serviceable, without attention or maintenance, fordecades. Understandably, environmental conditions often cause theelectrical characteristics of these air gaps to become unstable oversuch long periods of time. For example, penetration of moisture into thebackup air gap lowers the discharge voltage level and ultimately leadsto shorts. The insulation resistance between the signal conductors andground deteriorates, hindering regular performance of the network.Corrosion can induce shorts and cause corrosive destruction of themechanism. The reduced firing voltage of the air gap converts the gapfrom the secondary to the primary discharge path. Correct performance ofthe telecommunications network is thus compromised. These effects aremost pronounced when the air gap is directly exposed to the atmosphere,suffering seasonal as well as daily environmental effects, and furtherbecoming contaminated by air pollution, insect infestation, and soforth. Even when efforts are made to isolate the air gap from theenvironment, such as locating the device in a sealed container, it willbe appreciated that, over a course of years, moisture often still findsits way into the air gap.

Previous efforts to resolve this problem have included configurations inwhich the internal, normally gas-filled space was designed to act as anair gap upon venting of the gas. However, manufacturers ran intoproblems meeting the close tolerances required of such devices. Otherapproaches included improving the quality control and tolerances for theair gaps themselves: film thickness, die cutting quality of the film,air-gap diameter, anti-humidity coating, and so on. This increased thecost and manufacturing difficulty for these already intricate devices,but still left them vulnerable to the effects of humidity. Similarly,efforts at encapsulation were unsuccessful, whether using waxes, pottingcompounds, conformal coatings, encapsulants, gels, and so forth, all ofwhich tended to penetrate or migrate into the air gap and change thedischarge voltage levels.

A need therefore remains for an improved gas tube vent-safe device thatcan readily and inexpensively be utilized in place of existing air gapvent-safe mechanisms, and which will be reliably environmentally stableover extended periods of unattended service life. Advantageously, thevent-safe device should also be functionally compatible with the latestenvironmental sealing and encapsulation technologies, such as gelencapsulation, to support advances in these technologies and to provideimproved environmental isolation of the entire gas tube assembly. Thepresent gas tube vent-safe apparatus fulfills the above needs andpurposes. It provides a new and improved vent-safe apparatus for gastube protectors, in which the air gap is replaced with a layer of solidmaterial having particular non-linear electrical resistivecharacteristics. In the preferred embodiment, a solid, carbon blackfilled polycarbonate based extrusion grade compound is used. The filmhas a thickness from about 0.001 inch to about 0.010 inch or more, andpreferably from 0.002 inch to 0.005 inch. The film is non-conductive,having an insulation resistance greater than 10⁹ ohms when placedbetween two electrodes, regardless of geometry. The breakdown voltage(V_(B)) of the film is greater than 600 and less than 1000 volts, andcan be controlled to a narrow band (e.g., 800<V_(B) <850 volts, orroughly twice the design breakdown voltage of the gas tube), if desired.(Once a discharge has fired through the film, subsequent breakdownvoltages tend to be lower). The initial breakdown voltage proves to belargely independent of contact -with encapsulating materials (e.g.,silicone gel). Because the film is a thin (1 to 5 mil) insulatingplastic, it can be readily substituted for the fusible insulatingplastic films in existing designs, such as described in the '047 patentabove. In addition to extreme environmental stability (even whenimmersed in water the breakdown voltage and insulative properties of thefilm do not change significantly), the invention significantly improvesand simplifies manufacturing tolerances and procedures by eliminatingthe need to form precise holes and precisely position them in the gastube vent-safe structure. The preferred plastic material has a high heatdeflection temperature (ASTM D648), so that it avoids possibledeformation during thermal exposure in manufacturing, and exhibits lesscreep under compression and during temperature cycling.

A major feature of the present invention has to do with the dischargemechanism itself. Filled polymer films have been used in other technicalareas for discharging static electricity (e.g., such as used fordischarging static electricity in small personal computers). See, forexample, U.S. Pat. Nos. 4,977,357 (Shrier, issued Dec. 11, 1990) and5,068,634 (Shrier, issued Nov. 26, 1991). However, these have been lowenergy applications where the devices were designed for reliablerepeatability after many discharge events. That is, the performance hadto be non-destructive. A major distinction, and an important new featureof the present invention, is the realization and expectation that thepresent device will perform in a manner which will be destructive toitself. By making this a feature of the present invention (which isacceptable since this is a backup device that normally should not becalled upon to fire), the present invention can handle and dischargehigh voltage pulses having significant energy, such as caused bylightning pulses. In contrast, prior art devices in other technicalapplications have not been considered capable of handling such impulses.This has important implications. The actual discharge mechanism is aplasma which the high energy of the electrical pulse forms through theplastic film, once the plastic film begins to conduct. This plasmaresults in a nearly direct short to ground, which is required foreffective protection in telecommunications protector devices, andclosely mimics the performance of a normal gas tube. This suddenplasma-induced increase in conductivity (or reduction in resistance)provides a voltage foldback effect to an extent not seen innon-destructive static load situations, where similar films have beenused in other technologies, as mentioned.

This leads to an additional advantageous feature of the presentinvention. In another preferred embodiment, the vent-safe gap (andpreferably the entire gas tube device) is encapsulated in anenvironmentally sealing gel. A telecommunications terminal showing sucha gas tube (but without the present vent-safe mechanism) encapsulated ina gel, is disclosed, for example, in U.S. patent application Ser. No.776,501 (Baum et al., filed Oct. 11, 1991), assigned to the assignee ofthe present invention, the disclosure of which is incorporated herein byreference for all purposes. When a gas tube having a vent safe mechanismaccording to the present invention is thus environmentally sealed, thegel encapsulant advantageously protects the vent-safe mechanism fromenvironmental contaminants, excludes oxygen from the region of theplasma discharge, and acts as a heat sink. This gel encapsulated plasmadischarge substantially reduces the degradation of surroundingmaterials, prevents combustion, and draws thermal energy away from localhot spots. It is therefore an object of the present invention to providenew and improved methods and apparatus for providing vent-safeprotection for telecommunications gas tube protectors, and moreparticularly for providing gas tube vent-safe methods and devices whichinclude a first electrode for electrical connection to a terminal on thegas tube protector, a second electrode for electrical connection toanother terminal on the gas tube protector, and a non-gaseous,non-linear resistive material separating the electrodes, the nonlinearresistive material being substantially non-conductive when theelectrical potential between the electrodes is less than a predeterminedbreakdown voltage V_(B), being conductive when the electrical potentialis greater than V_(B), and supporting a plasma discharge therethroughafter becoming conductive to effect a sudden increase in conductivitybetween the electrodes for discharging high energy with a plasma voltagefoldback functionally analogous to the foldback behavior of the gas tubeprotector; wherein the first electrode may be at least a portion of thefirst gas tube terminal and thus located thereon; wherein thepredetermined breakdown voltage V_(B) may be greater than the designedbreakdown voltage of the gas tube protector at least prior to the firstdischarge through the non-linear resistive material; wherein thenon-linear resistive material may be a solid, filled polymer film whichis a composition comprising a polymer and, dispersed in the polymer, aparticulate conductive filler; wherein the film may be a carbon blackfilled polycarbonate based extrusion grade compound having a thicknessfrom substantially 0.001 to 0.010 inches or more, and preferably from0.002 to 0.005 inches; wherein the particulate conductive filler may becarbon black, the primary size of the bulk (90%) of the carbon blackfiller being in the 30 to 60 nanometer range and the total carbon blackcontent being 3 to 50% by weight of the total composition; wherein theelectrodes and the non-linear resistive material may be environmentallyencapsulated to protect them from environmental contaminants, to excludeoxygen from the plasma discharge, and to act as a heat sink to drawthermal energy away from local hot spots; wherein the encapsulant may bechemically inert to the film material; wherein the encapsulant may be agel; which may include a third electrode for connection to a thirdterminal on the protector; wherein at least part of at least one of theelectrodes may be at least partially rolled away from another of theelectrodes; and to accomplish the above objects and purposes in aninexpensive, uncomplicated, durable, versatile, and reliable method andapparatus, inexpensive to manufacture, and readily suited to the widestpossible utilization in telecommunications protector circuits.

With reference to the drawings, the new and improved gas tube vent-safemethod and device for telecommunications systems will now be described.FIG. 12 schematically illustrates a typical telecommunications circuit100 incorporating a gas tube 102 in a telecommunications line 104. Thegas tube protector 102 has end terminals 108 and 110 (FIGS. 13 and 16)for connection to the tip and ring sides of the telecommunicationscircuit, and a center ground terminal 112. The main body of the gas tubeprotector 102 is a durable plastic or ceramnic shell 114 (FIG. 13). Theinterior of the tube 102 contains an ionizable gas 116 which ionizes toform a discharge plasma at a predetermined design potential, such as350-450 volts, as indicated in FIG. 15.

FIG. 14 shows a typical prior art air gap gas tube vent-safe device 118.The end terminals 120 and 122 of device 118 also function as theelectrodes for the air gap vent-safe operation. Each of the endterminals/electrodes 120, 122 has a non-conductive film 124 that isperforated by holes 126 and which separates the electrodes 120, 122 froma ground electrode 128 which is connected to the center ground terminal130 of the gas tube 118. As already indicated, such air gap vent-safemechanisms are well known.

FIG. 15 illustrates the typical breakdown voltage V_(B) for a gas tube(usually around 350-450 volts), and the corresponding breakdown voltagefor the air gap vent-safe system 118. As illustrated by the arrows inFIG. 15, pointing respectively left and right, water which invades theholes 126 will reduce the breakdown voltage of the air gap vent-safedevice; oil will increase it. Thus, the deleterious effects ofenvironmental pollution, humidity, insect infestation, etc., can causethe air gap vent-safe device 118 to start firing at voltages comparableto those of the gas tube. This is effectively a system failure. On theother hand, efforts by the present inventors to seal the holes 126 fromenvironmental effects by gel encapsulation, for example, have inevitablyresulted in oil bleeding from the gel into the holes 126. This adverselyraises the breakdown voltage beyond the specification design limit.

The gas tube vent-safe device 138 illustrated in FIGS. 16-19 overcomesthese prior art limitations. In particular, the insulating film 134 issolid, not perforated. Thus, it is essentially immune to environmentalcontamination. Similarly, it can readily be encapsulated, such as in agel 136 (FIG. 21), without changing the design breakdown voltage of thedevice. Encapsulant 136 is selected of a material which is chemicallyinert to the film 134. For example, when the film is a polycarbonate, asilicone gel would be appropriate.

In the embodiment illustrated in FIGS. 16-19, the end terminals 108 and110 of the gas tube protector device 102 also function as electrodes forthe vent-safe components of the device. On the side of the film 134opposite the electrodes 108 and 110 is a ground electrode/film retainer140 connected to the ground terminal 142 on the gas tube. Furtherimprovement of vent-safe performance is realized by judicious geometricdesign of the supporting ground electrode/film retainer 140 (FIG. 18) toproduce controlled uniformity in the electric field which is developedthroughout the film material 134 between the ground electrode 140 andthe opposing gas tube electrode 108, 110 before and during breakdown. Ifno special attention were paid to this aspect, the possibility of highvariance in V_(B) exists. For example, in certain existing vent-safedesigns, sharp edge discontinuities occur on certain stamped metalparts, producing uncontrolled field non-uniformity. Even when otherparameters such as spacer material thickness and/or perforation holediameters in certain air gap designs are tightly controlled, slightmanufacturing differences in electrode material edges of improper designcan yield unacceptable V_(B) variance. Consequently, the preferredembodiment of the present invention incorporates such geometric design(in addition to the film material) in order to further improveperformance. In FIG. 18, the ends 144 (only one of which is shown) ofthe ground electrode 140 are partially rolled away from the opposing gastube electrode. This carries the sharp edge discontinuities of theground electrode 140 away from the curved surface of the gas tubeelectrode, thus reducing localized field enhancement in the vicinity ofthe edges and producing smooth curved electrode surfaces at the minimumseparation distance of the opposing electrodes. It also renders the partboth simple to manufacture, without extreme tolerance constraints, andaffords controlled, repeatable field uniformity for improvedperformance.

Device 138 may also be provided with electrodes which are distinct fromthe terminals 120 and 122 and are electrically connected thereto, suchdistinct electrodes also being located on the side of the non-linearresistive film 134 opposite the ground electrode. FIG. 20 illustratessuch an alternative gas tube vent-safe device 148 having electrodes 150'and 152' respectively electrically connected to the gas tube endterminals 150 and 152, and a ground electrode 140 connected to the gastube ground terminal 112. Electrodes 150, 152, in a fashion similar todevice 146, are separated from ground electrode 140 by a film 154 whichillustratively is the same as film 134.

FIG. 21 shows the gas tube vent-safe device 102 encapsulated in anenvironmentally protecting sealing gel 136. The gel encapsulant 136 notonly protects the device 102 from the environmental contaminants, butalso excludes oxygen from the region of the plasma discharge andconducts heat away therefrom (acting as a heat sink). This substantiallyreduces the degradation of surrounding materials, prevents combustion,and attenuates local hot spots. Such gels are preferably selected frommaterials which are chemically inert to the film material 124, 134.Proper selection of the gel material may also promote gradual, partial"healing" of the film 124, 134 in the damaged region of a plasmadischarge as the oil filler in the gel migrates to that region of thefilm.

The non-linear resistive films 124 and 134 are selected of a materialwhich is substantially non-conductive when the electrical potentialbetween the electrodes is less than the desired breakdown voltage V_(B).The film is thus non-conductive in that state, having an insulationresistance greater than 10⁹ ohms. Preferably, for telecommunicationsdevices, the breakdown voltage V_(B) is greater than 600 and less than1000 volts, and particularly in the vicinity of 800-850 volts.

In analyzing and developing a suitable nonlinear resistive film, it wasdiscovered that a homogeneous distribution of a rising electrical fieldcan be obtained through the dispersion of small conductive particles ina non-conductive matrix, e.g., carbon black in a polymer. This in turnleads to more controllable high voltage discharges through solidmaterials. Nonlinear resistive materials are already used as electricalstress dissipating layers at abrupt transitions in high voltageapplications.

Suitable non-linear resistive materials are prepared from a compositionwhich comprises a polymer and, dispersed in that polymer, a particulateconductive filler. In order to achieve an insulation resistance in useof greater than 10⁹ ohms, the resistive material has a resistivity of atleast 1×10⁶ ohm-cm, preferably at least 1×10⁷ ohm-cm, especially atleast 1×10⁸ ohm-cm. The type of polymer used is dependent on the desiredphysical properties of the resistive material in use, the type ofparticulate conductive filler, the anticipated use conditions, as wellas other factors such as ease of manufacture, maximum exposuretemperature, and chemical resistance. Either thermoplastic orthermosetting polymers may be used. Polymers which are particularlyuseful are those which can be formed, for example by extrusion,calendaring, casting, or compression molding, into relatively thinfilms, e.g., 0.001 to 0.010 inch (0.025 mm to 0.25 mm), and preferably0.002 to 0.005 inch (0.05 mm to 0.13 mm). Particularly suitable polymersinclude polycarbonates .

Dispersed in the polymer is a particulate conductive filler, i.e., amaterial which has a resistivity of less than 10⁻¹ ohm-cm, preferablyless than 10⁻² ohm-cm, particularly less than 10⁻³ ohm-cm. Among thoseparticulate fillers which may be used are carbon black, graphite,metals, metal oxides, or any of these materials coated onto at leastpart of an insulating particle such as a glass or ceramic particle. Asingle type of particulate filler may be used or the resistive materialmay comprise a mixture of two or more different fillers or two or moredifferent sizes or types of the same filler. Generally particulateconductive particles which are suitable for use in the invention have anaverage particle size, i.e., the size of the primary particle, of lessthan 1 μm, preferably less than 0.5 μm, particularly less than 0.1 μm,e.g. 0.01 to 0.09 μm. For some compositions, it is preferred that themajority of the particles of the particulate filler, i.e., at least 50%,preferably at least 60%, particularly at least 70%, especially at least80%, have an average particle size of 0.01 to 0.09 μm, preferably 0.02to 0.08 μm, particularly 0.03 to 0.07 μm. If the particles are fused orotherwise associated in the form of an aggregate, e.g. as carbon blackis, it is preferred that the aggregate size be less than 5 μm,preferably less than 3 μm, particularly less than 2 μm, e.g., less than1 μm. Depending on the type of particulate conductive filler and itsstructure, particle size, density, and conductivity, the amount ofparticulate conductive filler in the resistive material is 3 to 70% byweight of the total composition, preferably 3 to 50% by weight,particularly 15 to 45% by weight, especially 20 to 40% by weight. Whenthe particulate conductive filler is carbon black, the amount is often 3to 50% by weight of the total composition, particularly 3 to 35% byweight, especially 3 to 10% by weight.

The above criteria were met during experimentation with non-linearresistive film materials from LNP Engineering Plastics Inc. (Exton,Pa.), available under the trade name "Stat-Kon." One suitable materialwas Stat-Kon DX7, a carbon black filled polycarbonate based extrusiongrade compound with volume resistivity between 10E7 and 10E12 ohm-cm.Films were obtained at a 10 mil thickness and measured 10E7 ohms ininsulation resistance at 250 vdc using the film thickness as electrodeseparation. In fact, any location of the two electrodes on the filmalways gave the same insulation reading. Thinner films were obtained bycompressing the 10 mil film on a hot press down to 2.5 to 4.0 mil.

As a test, these 2.5 to 4.0 mil films were inserted between the metalspring terminal/contact accessories of commercially availablethree-element gas tube integrated vent-safe/fail-safe protectors andtested for performance according to Bellcore TR-TSY-000073, whichBellcore specification is incorporated herein by reference for allpurposes. Insulation resistance as measured in the device remained atthe high levels as measured before on the film only, and thetip-to-ground or ring-to-ground breakdown voltage of the vented gas tubeprotector (through the thin film) varied from 700 volts to 900 volts,whether or not encapsulated in silicone gel. However, gel encapsulationsubstantially reduces the oxygen source needed for combustion, and itacts as a heat transfer medium to effectively draw the thermal energyaway from local hot spots. In this way, a smooth and safe operation issecured during these high energy transfers, substantially reducing thedegradation of surrounding materials (gel encapsulated plasmadischarge). As encapsulated in silicone gel, there was no interferencewith the fail-safe mechanical spring mechanism during a power-cross test(1A, 1000V, 60 Hz), a homogeneous heating took place without visiblesparking or material degradation, and the metal spring moved through themelting polycarbonate film to form a metalto-metal contact, dumping thecurrent to ground.

FIGS. 22, 23 and 24 depict the IV-curves for Stat-Kon DX7 films ofdifferent thicknesses. The interesting and very useful features of aStat-Kon DX7 type material are that the breakdown voltage levels remainrelatively independent (as compared to an air gap) from the filmthickness, the insulation resistance remains at a high level, and forthin films around 3 mil, the trigger current is in the micro amp range.FIG. 25 shows the IV-curve of a 2.5 mil pressed Stat-Kon DX7 film asreplacement for the air gap of a commercially available three-elementgas tube vent-safe device. FIG. 26 depicts the IV-curve for the moreconductive 15 mil Stat-Kon DX3 film (resistivity 103 to 106 ohm-cm).Having an insulation resistance around 10E6 Ohms makes the DX3 film lesspreferable for telephone circuit applications.

As pressing of thin films lead to inconsistencies with regard to filmthicknesses and electrical parameters, extrusion of thin films waspursued using polycarbonate based compounds with carbon black loadingsfrom 3% to 10%. The carbon black used had a primary particle size mostlybelow 75 nanometers and an aggregate particle size centered around 0.5microns. An example of such a film is the Stat-Kon DX9 material(resistivity 109 to 1012 ohm-cm). FIG. 27 depicts a typical IV-curve forthis material. FIGS. 28-30 depict the electrical impulse breakdownbehavior as a function of current loading for this material. Materialanalysis of a single sample from the trial extrusion indicated that thematerial comprised 3 to 10% by weight carbon black with a particle sizeof 0.030 to 0.069 nm, 65 to 70% by weight bisphenol-A-polycarbonate, and1 to 3% by weight other filler.

As may be seen, therefore, the vent-safe apparatus of the presentinvention provides numerous advantages. Principally, it provides anenvironmentally stable apparatus for a telecommunications gas tubeprotector. By eliminating the conventional air gap, and especially whenencapsulating (such as in a gel) the breakdown voltage V_(B) remainsreliably stable over very extended periods of time. Once the gas tubefails and the present invention fires in its place, this will, ofcourse, damage the film 134 in the region of the discharge. Theinability of such non-linear resistive films to repeatably conduct suchhigh currents without damage has heretofore been seen as aninsurmountable barrier. As taught by the present invention, however,since under normal conditions the vent-safe apparatus of the presentinvention never fires, and the apparatus is intended to be replaced oncethe gas tube 102 has failed, damage to film 134 is acceptable. In fact,if the film carbonizes leaving a low resistance path, this may actuallybe advantageous since it will assist in identifying a failed gas tube.In other words, it has been recognized that, in this technology,repeatability can be sacrificed for performance and environmentalstability. This is a major conceptual and functional breakthroughheretofore unavailable.

Of course, various modifications of the ventsafe apparatus are possible.For example, other nonlinear resistive materials having electricalcharacteristics similar to the preferred filled polycarbonate films maybe found suitable. These can include non-gaseous, but not necessarilysolid, materials such as, for example, suitable gels having the desiredelectrical properties. In a humid environment, a nonencapsulated carbonblack filled nylon 11 film could be used instead, with excellentresults. Since such a film is inert to mineral oil based gels and tosilicone gels, it could be gelencapsulated as well. It also has a sharpmelting point, for improved fail-safe performance in applications to bedescribed below. In another modification, the vent-safe apparatus can beused with two element gas tubes, thus requiring only two electrodes onthe vent-safe apparatus itself.

In addition to vent-safe mechanisms, gas tube surge arrestors frequentlyare also equipped with failsafe mechanisms. When an arrestor issubjected to a current surge condition over a long period of time, asmight occur for instance due to a power line crossing, the heatgenerated by the arrestor may be sufficient to present a fire hazard. Toprevent the foregoing, the fail-safe mechanism short circuits thecurrent to ground when the arrestor is subjected to a thermal overload.A commonly employed means for establishing the short circuit includes aspring contact that is normally maintained in an inactive position bysolder or other meltable material. When a thermal overload conditionoccurs, the material melts and permits movement of the spring to anactive short-effecting position. In the aforesaid prior art arrestor themeltable material does not itself form the short circuit. However, U.S.Pat. No. 4,851,946 discloses a different type of fail safe thermaloverload mechanism in which molten solder material directly forms ashort circuit between ground and line electrodes when the arrestor issubjected to a thermal overload.

The fail-safe thermal overload mechanism of the present invention issimilar to that disclosed in the above noted prior patent in that itemploys solder material that melts and directly forms the desired shortcircuit when the arrestor is subjected to a thermal overload. The failsafe mechanism is highly reliable in operation and relativelyinexpensive. In a preferred embodiment the fail safe mechanism includessolder flux upon the outer surface of the housing of the arrestor, asolder billet overlying the arrestor housing, and channel and springmembers that overlie the billet and bias it to a location closelyadjacent and preferably abutting the arrestor body. Solder flux mayadditionally or alternatively be provided upon the inner and/or outersurfaces of the solder billet, and/or within billet. A preferred flux isa rosin based one that under normal (i.e., no thermal overload)conditions, coats and protects the surfaces to which it is applied, andhas good dielectric properties and acts as an insulator. When the soldermelts under thermal overload conditions, the flux causes the moltensolder to thoroughly wet surfaces of the arrestor housing and thechannel member of the fail-safe mechanism so as to facilitatepreferential flow of molten solder from the solder billet to one or morelocations establishing a highly conductive, low resistance short circuitbetween the arrestor electrodes. When the arrestor housing is ofcylindrical shape, as is customary, the channel member is preferably ofgenerally Vshaped configuration and has first and second sections thatextend angularly relative to each other and meet at an apex thatoverlies and extends generally parallel to the central axis of thearrestor housing. When the arrestor is subjected to a thermal overload,the channel member permits relatively free flow of molten solder fromthe solder billet in a first direction, which in the illustrativeembodiment is generally parallel to the longitudinal axis of thearrestor housing, while limiting flow of the molten solder in a second,transverse direction.

Referring now to FIGS. 31-38 of the drawings, the surge arrestor 156 isillustratively of the type having a cylindrical housing 158 thatincludes diskshaped line electrodes 160 at its opposite ends, adisk-shaped ground electrode 162 intermediate the length of the housing,and insulating material 164 intermediate electrode 162 and each of theline electrodes 160. Arrestor 156 may and illustratively does furtherinclude pin-type lead elements 166 that extend from respective ones ofthe electrodes. At least some, and illustratively substantially all, ofthe exterior surface of housing 158 is overlaid by a film, foil orcoating of solder flux material 168 which is indicated in the drawingsby stippling. Flux material 168 is preferably of a rosinbased type thatunder normal temperatures of housing 158 has strong dielectricproperties, and protects the housing and other members engaged therebyfrom contaminants and other materials such as soft textured encapsulants170 (e.g., gels, oils, greases, etc.) such as shown in FIG. 38. Underthermal overload conditions the flux greatly facilitates flow of moltensolder along the housing and other members engaged thereby. An exampleof flux of the foregoing type is that sold by Alpha Metals of JerseyCity, N.J., under the type designation R100, and is comprisedessentially of natural rosin, alcohol and in certain other formulations,proprietary activators.

A channel-shaped solder billet 172 overlies and extends longitudinallyof the upper surface of housing 158. Billet 172 is illustratively ofinverted V-shaped configuration and has opposite side sections thatextend angularly downwardly from each other and from an apex 24 upon theupper surface of the billet. The undersurface of the billet preferablyand illustratively has a concave contour complementary to thecylindrical outer surface of housing 158, and may have a film or coating168-1 of flux 168 thereon. The thickness of billet 172 is greatest inthe portion thereof underlying apex 174 and is of a lesser magnitudeadjacent the opposite side edges of the billet. The upper surface of thebillet has a semispherical protuberance 176 generally centrally thereof,and may have a foil, film or coating 168-2 of flux 168 upon such uppersurface.

Alternatively or additionally, flux material 168 may be present upon theundersurface of a conductive channel member 178 of the thermal overloadmechanism. In keeping with billet 172, member 178 is preferably ofgenerally channel-like V-shaped configuration, and has opposite sidesections that closely overlie the opposite side sections of billet 172.A centrally located semispherical socket 180 upon the upper surface ofmember 178 receives billet protuberance 176 and allows limited adjustivemovement of billet 172 relative to member 178 and arrestor housing 168.

The aforesaid components of the fail-safe mechanism are secured to eachother and to arrestor housing 158 by a generally U-shaped resilientspring member 182. Spring 1 82 has generally horizontallyextending upperand lower legs 184;, 186 that extend in parallel relationship to eachother from a generally vertically extending section 188. Legs 184, 186have vertically aligned openings 190, 192 adjacent their free outerends. The center one of the conductive pins 166 of arrestor housing 158extends downwardly through opening 192 of leg 186. Opening 190 of upperspring leg 184 receives the socket 180 of channel member 178, andpermits limited adjustive movement of channel member 178 and underlyingsolder billet 172 relative to arrestor housing 158 and spring 182.Spring forces imposed by spring 182 upon the assembled components biasmember 178 and billet 172 downwardly to a position wherein billet 172 isfirmly seated upon the upper surface of arrestor housing 158.

As is best shown in FIGS. 34-36 of the drawings, the opposite side edgesof member 178 preferably extend beyond the opposite side edges of theunderlying solder billet 172, and the opposite end portions of member178 preferably extend beyond the opposite ends of billet 172 and beyondthe opposite ends of arrestor housing 158. In the embodiment of FIG. 35the central portion of billet 172 overlies ground electrode 162 ofarrestor 156, and opposite end portions of billet 172 overlie respectiveadjacent ones of line electrodes 160 of arrestor housing 158.

The embodiment of FIG. 34 differs from that of FIG. 35 primarily in thatthe opposite ends of billet 172 portions are spaced axially inwardlyfrom, and do not overlie, electrodes 160. Consequently, while the solderflux employed in the FIG. 34 embodiment may be of the previouslydescribed flux 168 type, other flux not having the dielectric insulatingproperties of flux 168 may instead be used in the embodiment of FIG. 34.

When the arrestor 156 of FIG. 34 is subjected to thermal overload solderbillet 172 melts and molten solder from the billet flows axially, aswell as in other directions, along the exterior surface of arrestorhousing 158 into engagement with line electrodes 160 so as to therebyestablish a dense and highly conductive short circuit between each ofsuch electrodes and the ground electrode 162 underlying the billet. Whenthe solder flux is of the preferred type that causes the molten solderto thoroughly wet housing 158 of arrestor 156, the molten solder willflow not only to the annular surfaces of the electrodes, but also to theouter end surfaces of line electrodes 160. This will normally occurirrespective of the orientation of arrestor housing 158. Tin plating theground electrodes and the undersurface of the channel shaped billetretainer 178 also improves the wicking of the molten solder.

The axial flow of molten solder from billet 172 is enhanced by thegenerally V-shaped configuration of channel member 178. As is shown inFIG. 36, the opposite side edges of member 178 preferably extendoutwardly beyond the opposite side edges of billet 172, and normally arespaced slightly above the underlying cylindrical surface of arrestorhousing 158. When solder billet 172 melts in response to a thermaloverload condition, molten solder passes initially from both theopposite ends and the opposite sides of billet 172 and channel member178. This initial passage of molten solder from the billet, inconjunction with the downward biasing force imposed upon member 178 byspring 182, causes member 178 to descend until its opposite side edgeportions engage the underlying surfaces of arrestor housing 158. Suchengagement restricts, if not altogether stops, the passage of moltensolder from beneath the opposite side edge portions of member 178, whichin turn causes preferential flow of the molten solder parallel to thecentral axis of arrestor housing 158 through the opposite ends of thespace overlaid by member 178 and to electrodes 160.

While in the illustrative embodiments solder flux 168 is provided uponsubstantially all of the exterior surfaces of arrestor housing 158, theflux might instead be applied, in bands or the like, only to selectedsurfaces of the housing upon which solder is to flow.

In lieu of solder flux that is applied separately, the solder flux maybe integral with the solder material of billet 172.

If the exterior surface of housing 158 were flat or of some othernon-arcuate shape, channel member 178 might be U-shaped rather thanV-shaped.

Another embodiment of a fail-safe mechanism 194 for a surge protector196 is shown in FIG. 39 of the drawings. Mechanism 194 includes aretainer 195 having a central section that is welded or otherwisesecured upon the cylindrical body of surge protector 196. Protector 196has live electrodes 200 at its opposite ends, and a centrally disposedground electrode 202. Resilient legs 204 extending outwardly fromopposite sides of retainer 195 overlie the aforesaid electrodes and anintervening strip of heat sensitive non-conductive plastic film 206 orsimilar material that melts or otherwise disintegrates when protector198 is subjected to a thermal overload. Melting of film permitsengagement of resilient legs 204 with the underlying electrodes 200,202, which in turn shunts the current to ground via a pin type groundterminal 208 projecting downwardly from electrode 202.

FIGS. 40-51 disclose another embodiment of a terminal block andfail-safe mechanism in accordance with the invention. Components similaror identical to ones shown and described previously herein areidentified by the same reference numerals, with the addition of a primedesignation.

The terminal block identified in its entirety in FIGS. 40-42 by thenumeral 12' includes a base 14' that may be of any desired length. Base14' illustratively extends horizontally and is of generally rectangularshape. A multi-core cable 16' extends into an end of base 14'. Althoughit may be mounted upon other structures, and in other ways, block 12'illustratively is mounted upon a perforate panel 210 of a pedestal mount(not otherwise shown). The means mounting the block upon panel 210illustratively includes a bracket 212 that is secured to the uppersurface of the panel by threaded fasteners 214. Generally U-shapedchannels 216 (only one of which is shown in FIG. 40) upon opposite sidesof bracket 212 receive flanges 218 that project outwardly from oppositesides of base 14'. The flanges restrict lateral and upward movement ofbase 14' relative to bracket 212, while permitting longitudinaladjustive movement of the base relative to bracket 212 and panel 210.The base's capability for such movement facilitates vertical alignmentof threaded fasteners 220, that extend through a slot 222 adjacent anend of base 14', with underlying bores 224 in panel 210. Tightening offastener 220 secures the rightmost (as viewed in FIG. 40) end of base14' to panel 210. An internally threaded socket 226 opening from theupper surface of bracket 212 receives a threaded fastener 228 thatreleasably secures the leftmost end of base 14' to bracket 212, and thusto panel 210.

When fastener 228 is tightened its head conductively engages a groundcontact 230 of a ground strip 232 within a channel 234 that extendslongitudinally of base 14' and underlies the driver modules 50' uponbase 14'. Ground strip 232 connects to a ground eyelet which isconnected by a ground clip to the cable shield when shielded cable isused.

A plurality of pairs of upstanding slotted socket members 238 upon base14' receives the lower end portions of insulation displacing connectors24' that extend in substantially the same angled "overlapping"relationship to each other as the connectors 14 of the FIGS. 1-11embodiment. The connectors 24' differ from the connectors 24 in thatthey have tooth-like retainer elements 240 that resist upward withdrawalof connectors 24' from the slots of member 238, and also differ in thatthe central portion of connectors 24' have a slightly greater width thanthe width of connectors 24. Additionally, connectors 24' illustrativelydo not have a contact comparable to the contact 44 (FIG. 8) ofconnectors 24. Posts 56' extending upwardly from the rear part of theupper surface of base 14' are similar to the posts 56 except for theirhaving channels 242 that receive ribs 244 (FIG. 46) projecting inwardlyfrom opposite sides of the driver module chambers 54' that receive posts56'

Driver modules 50' are cantilever mounted uponrespective ones of theposts 56' for movement between upper and lower positions respectivelyshown in FIGS. 43 and 44. Vertical movement of a module 50' between suchpositions is effected by a screw-type fastener 58', illustratively andpreferably of the self-tapping type, which extends through an opening60' of the module and into a vertically extending blind bore 248 locatedin and opening from the upper end of post 56'. A collar 250 (FIG. 43)extending downwardly from the upper end of opening 60' facilitatesformation of the initial screw threads in bore 228 without "stripping"of such threads, and resists inadvertent complete removal of fastener58'.

Module 50' also differs from the module 50 of FIGS. 1-11 in variousother respects. The vertically extending rear wall of each mounting post56' has, upon its rear surface, a cam element 252 and an overlyingabutment element 254. The rear wall of the post receiving chamber 54' ofeach driver module 50' has a vertically extending slot 256 into whichelements 252, 254 project, and also has a flexible element 258 borderingone side of slot 256 and having adjacent its lower end a projection 260.When a driver module 50' is driven downwardly from its uppermostposition by rotation in the appropriate direction of self-tapping screw58', finger 258 is deflected laterally away from elements 232, 234 byengagement of projection 260 with such elements. W hen the module 50'reaches its lowermost position, finger 258 returns resiliently to asubstantially vertical position wherein its projection 260 underlies camelement 252. If fastener 58' is subsequently rotated in an opposite,"loosening" direction, cam element 252 deflects flexible element 258laterally (rightwardly, as viewed in FIG. 43) such that its projection260 clears cam element 252. As the lower end of element 258 passes abovecam element 252 resilient return movement of element 258 produces anaudible and tactile signal indicating to a craftsperson that the drivermodule occupies its upward position. If complete removal of a module 50'from base 14' is desired, this can be effected by a craftspersonmanually moving the module 50' upwardly, after fastener 58' has beenremoved from bore 248, since the projection 260 on finger 238 is thencanned outwardly by its engagement with cam element 254.

The sections of each pair of the insulation displacing connectors 24'that extend upwardly from each pair of socket members 238 are receivedwithin insulation displacing connector chambers 66' that communicatewith each other and with the passageways 70' through which service wires46' are introduced into module 50'. Each chamber 66' has at its upperend a test port area 66'a. The test port areas 66'a differ from the testports 66a of the FIGS. 1-11 embodiment in that each pair of adjacenttest ports 66'a has at its upper end a forwardly disposed sloping wall.262, and a rearwardly disposed vertically extending wall 264 havingnonaligned sections that are separated by a shoulder 266. Test clipscannot be secured to sloping wall 262. The test clips therefore must beapplied to the wall 264, and the shoulder 266 of such wall preventsinadvertent contact of adjacent test clips with each other.

The surge arrestors 268 carried by respective ones of the driver modules50' shown in FIGS. 40-51 are generally of the construction of the surgearrestor 196 shown in FIG. 39. However, the arrestors 268 illustrativelyhave resiliently flexible contacts 270 that extend from the opposite endcontacts of the cylindrical arrestor body and have generally circularenlarged free ends 272 that engage respective ones of the connectors 24'within modules 50' in all vertical positions of the driver modules. Thecylindrical body of each surge arrestor 268 is supported by and movablewith a carrier 70"within module 50'. When a module 50' is moved to itslower position, a pin-type ground contact 274 extending downwardly fromthe central ground contact of surge arrestor 268 is received within anunderlying pair of the resilient upwardly opening contacts 276 of groundstrip 232. This illustratively occurs, as shown in FIGS. 43 and 44, bothwhen driver module 50' occupies its lowermost position of FIG. 44, andalso when the driver module occupies a more elevated position as shownin FIG. 43. If desired, however, engagement between the contacts couldbe caused to occur only when module 50' occupies a lower position. Thisresult could be achieved by simply shortening the length of the surgearrestor contact 274.

FIGS. 50 and 51 of the drawings show an alternative embodiment of aterminal block that may be used when surge protection is not desired. Insuch embodiment there is no ground strip 232 or surge arrestor 268. Inlieu of a surge arrestor carrier the driver module 50" of FIGS. 50 and51 contains a nonconductive stud 277 that overlies the slot 234 thatwould house the ground strip if one were present.

Stud 277 also constitutes "lock out" means minimizing possibleaccidental use of an unprotected driver module 50" with a basecontaining a ground strip, The size of stud 277 is sufficiently greatthat if an unprotected module 50" were accidentally used in associationwith an "active" base containing a ground strip, stud 277 would abut theground strip and halt downward movement of module 50" before the modulereached its position shown in FIG. 51. The resistance to furtherdownward movement of the module would notify the telecommunicationscraftsperson of the erroneous use of module 50".

The socket members 238 shown in FIGS. 40-44 extend upwardly to a higherelevation than the members 18 of the first embodiment. This assists inprevention of moisture and/or other foreign matter engaging the lowerend portions of connectors 24', and also causes members 238 to act aspistons which pump sealant material upwardly when modules 50' are drivendownwardly. The cable wires 17' are preferably surrounded by factoryinstalled potting compound or similar protective material that isindicated by the stippling in FIGS. 43, 44, 50 and 51 of the drawings.

While preferred embodiments of the invention have been shown anddescribed, this was for purposes of illustration only, and not forpurposes of limitation, the scope of the invention being in accordancewith the following claims.

We claim:
 1. An insulation displacing connector, comprising:an elongatebody having opposite side edge portions, an upper edge portioninterconnecting said side edge portions, a conductor inlet opening belowsaid upper edge portion and a slot communicating with and extendingdownwardly from said inlet opening; wherein said side edge portionsconstitute primary spring elements, and further including first andsecond secondary spring elements bordering first and second oppositesides of said slot; and wherein each of said secondary spring elementseach has a first end connected to the elongate body of said connector,and extends in cantilever fashion from said first end thereof to anopposite free end thereof.
 2. An insulation displacing connectorcomprising:an elongate body having opposite side edge portions, an upperedge portion interconnecting said side edge portions, a conductor inletopening below said upper edge portion and a slot communicating with andextending downwardly from said inlet opening; and wherein said slotdecreases in width with increasing distance from said inlet opening. 3.An insulation displacing connector as in claim 2, wherein said slot hasdiscrete sections along the length thereof of progressively decreasingwidth.